1. Field of the Invention
The present invention relates, in general, to mass storage devices, and, more particularly, to software, systems and methods for implementing high performance disk drives using self-mirroring within the drive.
2. Relevant Background
Computing systems are used to manipulate and store large quantities of data used in commerce, government and research. While the instruction rate at which data processors can perform has increased dramatically over recent years, the input/output (I/O) rate at which data can be supplied to processors has not increased proportionately. Accessing mass data storage systems remains a critical bottleneck limiting the overall performance of many computing systems.
Mass data storage systems strive to provide high storage density with low latency access to the stored data. Disk drive manufacturers continue to provide increasingly higher densities of data storage in storage devices using magnetic, optical, magneto-optical and other storage technologies. Advancements in hard disk magnetic recording technology are enabling the doubling of disk capacity every year.
Disk drives typically comprise one or more disks or platters having a recording media formed on one or more of the disk surfaces. A read/write head attached to an actuator mechanism moves across the disk between inner and outer diameters while the platters spin. Read channel electronics read and write data onto the disk surfaces as well as reading formatting, control and servo data recorded on the disk surface. Servo control electronics coupled to the read channel and the actuator mechanisms use servo control data and high-resolution servo data (e.g., servo bursts) recorded on the media surface to locate particular tracks and align the head over the centerline of selected tracks in response to read/write commands.
By carefully controlling spin speed and actuator movement, data can be accessed with great precision. Although capacity improvements in early disk drives came from adding more platters within a single enclosure, more recently improvements arise from decreasing the track size and recording rate to improve the areal density of the disk drive system. Continuing improvements in media properties, read channel electronics, and servo control systems are expected to lead to continuing higher areal densities.
However, hard disk performance in terms of reduced latency is only improving 15% to 30% a year. Latency in a disk drive system is primarily determined by the seek time and the rotational latency. Other contributing factors to latency, including various processing time required to process commands, tend to be minor. Seek time refers to the time required to position a read/write head over a selected track on a disk drive surface. Rotational latency refers to the time required for the desired location on a track to rotate under the read/write head and is largely a factor of spin speed of the rotating media.
There is a continuing need for higher performance hard disk drives. To achieve high performance customers use multiple drives in RAID (redundant array of independent disks) configurations such as RAID level 0 and RAID level 1 mirroring. Mirroring allows a data set to be spread out or “striped” across many disk drives or spindles so that latency associated with accessing each drive can be overlapped. When choosing to spread data across many spindles customers often choose smaller capacity drives over larger capacity drives driven by overall solution cost and the total capacity needed. There is a trend today that individual drive capacity is larger than what customers need.
While mirroring across multiple drives has improved performance in multiple-drive systems, until now, only a few strategies have existed to reduce latency within the drive itself. The mechanics of the head and actuator mechanisms limit the acceleration and speed at which a head can be moved between inner and outer diameters of the disk. Hence, seek latency is difficult to reduce. However, smaller disks and “short-stroking” (i.e., causing the actuator to move over less than all of the disk surface) have been used to lessen seek latency. In the case of solutions like short-stroking, disk capacity is simply discarded to improve performance. It would be preferable to implement a system that could use this capacity productively to improve performance rather than simply throwing it away.
Rotational latency is conventionally addressed by increasing the rotational speed of the platters. In recent years spin speed has increased to 7200 rpm in consumer disk drives, while 10,000 rpm and 15,000 rpm drives are available in enterprise class drives. However, increasing spin speed has several drawbacks. Higher spin speeds create more vibration, oscillation, and media flutter making it correspondingly difficult to precisely position the head during read/write operations. Also, the read channel and servo electronics must be able to handle the increased data rate. Moreover, faster spinning drives require more power making them impractical for many portable electronic devices. As a result, increasing the spin speed of drives by itself is not expected to provide adequate performance improvements in the near future. Hence, a need exists to provide the benefits of higher spin speeds disk drives without the associated drawbacks that increase cost and reduce performance.